1. Field of the Invention
The present invention relates generally to probe devices and more particularly, to a probe device having a spring probe.
2. Description of the Related Art
Upon testing semiconductor chips, a tester is electrically connected with devices under test (hereinafter referred to as the “DUTs”) through a probe card, so that the tester can obtain the testing results of the DUTs by means of signal transmission and analysis. The conventional probe card is usually composed of a circuit board and a probe device, or further comprises a space transformer disposed between the circuit board and the probe device. The probe device has a plurality of probes arranged corresponding to contact pads of the DUTs, so that the contact pads can be probed by the probes at the same time.
FIG. 1 is an exploded plan view of a conventional spring probe 11 which comprises a needle 12, and a spring sleeve 13 sleeved onto the needle 12. FIG. 2 is a schematic sectional view of a probe card 14 using the spring probe 11. For the convenience of illustration, FIG. 2 is not drawn to the same scale with FIG. 1. The probe card 14 comprises a circuit board 15 and a probe device 16 having a probe seat 17 and a plurality of probes 11. For the convenience of illustration, only a small part of the circuit board 15 and the probe seat 17 and one of the probes 11 are shown in FIG. 2.
The needle 12 and the spring sleeve 13 of the probe 11 are connected in a way that a connection segment 132, which is provided near the bottom end of the spring sleeve 13, is pressed against the needle 12 and fixed to the needle 12 by welding, such as spot welding. As a result, the connection segment 132 has two convex portions 134 resulted from deformation of the connection segment 132 in the aforesaid press fixing process, and the convex portions 134 protrude over an outer cylinder surface 136 of non-pressed parts of the spring sleeve 13.
The probe seat 17 is composed of upper, middle and lower dies 171, 172, 173; however, the probe seat 17 may be provided without such middle die 172 but composed of the upper and lower dies 171, 173 only. The probe seat 17 has a plurality of installing holes 174 provided in the assembly of the dies 171, 172, 173 (only one of the installing holes 174 is shown in FIG. 2). In order that the spring probe 11 can be installed into the installing hole 174 through a top surface 175 of the completely assembled probe seat 17 and rotatable unlimitedly in the installing hole 174 when probing a DUT, the installing hole 174 is configured as a circular hole with a radius greater than the maximum distance between each convex portion 134 and the center of the spring probe 11.
After the probe device 16 is assembled completely, the circuit board 15 is disposed on the top surface 175 of the probe seat 17. The top end of the spring sleeve 13 is electrically connected with a contact pad of the circuit board 15. The bottom end of the needle 12 is adapted to probe a contact pad of the DUT. Specifically speaking, the top end of the spring sleeve 13 is abutted against the circuit board 15, and the spring sleeve 13 is provided with two spring sections 138 which are compressible elastically; besides, the connection segment 132 of the spring sleeve 13 is fixed to the bottom section of the needle 12, and a clearance 18 is provided between the top end of the needle 12 and the circuit board 15, i.e. between the top end of the needle 12 and the top end of the spring sleeve 13. Therefore, when the bottom end of the needle 12 contacts the contact pad of the DUT and correspondingly feeds forward, the needle 12 will retract backwards, such that the spring sleeve 13 will be compressed. In this way, the probe 11 can positively contact and electrically connect the contact pad of the DUT; besides, by means of the cushioning effect provided by the spring sleeve 13, an exceeding contact force, which may cause damage or heavy wear of the contact pad of the DUT or the needle, can be prevented.
The outer radius of the aforesaid spring probe 11 is very small, which is usually in a range of several tens micrometer to a little more than one hundred micrometer, and the aspect ratio of the spring probe 11, i.e. a ratio of height to width thereof, is very large, which is usually in a range of 10:1 to 100:1. Besides, except for the convex portions 134 which are relatively closer to the inner wall of the installing hole 174, the other parts of the spring sleeve 13 are quite distanced from the inner wall of the installing hole 174. Therefore, the spring probe 11 is liable to deflect and bend when the bottom end of the needle 12 receives external force, as shown in FIG. 3. This phenomenon may result in problems of inaccurate alignment, unstable probing pressure, and the tendency of fracture of the probe. If the probe is fractured, more problems will be caused, such as difficulties in maintaining and replacing the probe.
On the other hand, a juncture 176 of the upper and middle dies 171, 172 is arranged corresponding in position to one of the spring sections 138 of the spring sleeve 13, and a juncture 177 of the middle and lower dies 172, 173 is arranged corresponding in position to the other spring section 138 of the spring sleeve 13. If the dies 171, 172, 173 are not well aligned with each other due to assembly error to cause unevenness on the inner wall of the installing hole 174 at the junctures 176, 177, the spring sections 138 are liable to contact the uneven junctures 176, 177 and then jam at the uneven junctures 176, 177. In this case, the spring probe 11 will need maintenance and have subsequent problems, such as difficulties and time-consumption in maintenance.